Lesch Nyhan syndrome is an X-linked recessive disorder of purine metabolism causing overproduction of uric acid. There is central nervous system involvement resulting in abnormal mental behavior including mental retardation and a compulsive form of self mutilation. The disease is caused by a deficiency of hypoxanthine-guanine phosphoribosyl transferase (HGPRT), the enzyme that converts the free bases hypoxanthine and guanine to nucleotides. While the mechanism of the uric acid overproduction in HGPRT-deficient cells is well understood, little is known about how the HGPRT deficiency causes the unusual mental behavior. There is recent evidence of dysfunction of dopminergic nerve terminals. For example, there is decreased levels of dopamine, homovallinic acid, dopamine beta hydroxylase and dopa decarboxylase in brains of Lesch Nyhan patients. Our long term objective is to understand the molecular mechanism by which a deficiency of HGPRT causes neuronal dysfunction. Our approach to this objective will be to study the effect of an HGPRT deficiency on the ability of a clonal cell line to differentiate into neurons and to synthesize and release neurotransmitter. The clonal cell line is PC12, a rat pheochromocytoma. PC12 cells contain dopamine and acetylcholine and they secrete each by a Ca squared plus -dependent process. After treatment with nerve growth factor, PC12 cells extend neurites and acquire the appearance of neurons. These properties make PC12 particularly well suited for studying the consequences of an HGPRT deficiency on neuronal function. We have obtained mutant PC12 cells deficient in HGPRT activity. We will determine whether the HGPRT-deficient PC12 cells differ from wild type PC12 with respect to: 1) the ability to differentiate into neurons; and 2) the synthesis, vesicular storage and release of dopamine and acetylcholine. These studies will establish whether the HGPRT deficiency is harmful to dopaminergic function because it affects neuronal development, or alternatively neurotransmitter metabolism in fully developed neurons, and whether the adverse effect is specific to dopamine metabolism or is non-specific in that it also affects acetylcholine metabolism.